$$ Last token of the last line received by the shell.
$? Success/fail status of the last operation.
$^ First token of the last line received by the shell.
$_ Current pipeline object in a pipelined script block.
$args Array of parameters passed to the script, function, or scriptblock.
$error Array that holds the (terminating and non-terminating) errors generated in the shell.
$home User’s home directory
$host Means by which scripts can access the APIs and implementation details of the current host and user interface.
$lastExitCode Exit code of the last command—can be explicitly set by scripts, and is automatically set when calling native executables.
$pid Process ID of the current PowerShell instance.
$profile Location and filename of the PowerShell profile for this host.
$psHome Installation location of PowerShell.
$pwd Current working directory.
$shellId Shell identifier of this host.